1. Field of the Invention
The present invention relates to the field of flat panel display screens. More specifically, the present invention relates to the field of flat panel field emission display (FED) screens.
2. Related Art
In the field of flat panel display devices, much like conventional cathode ray tube (CRT) displays, a white pixel is composed of a red, a green and a blue color point or "spot." When each color point of the pixel is excited simultaneously, the pixel appears white. To produce different colors at the pixel, the intensity to which the red, green and blue points are driven is altered using well known techniques. The separate red, green and blue data that correspond to the color intensities of a particular pixel are called the pixel's color data. Color data is often called gray scale data. The degree to which different colors can be achieved within a pixel is referred to as gray scale resolution and is directly related to the amount of different intensities to which each red, green and blue point can be driven.
Field emission display (FED) screens, like CRT displays, utilize phosphor spots to generate the red, green and blue color points of a pixel. Often, during manufacturing, the characteristics of the phosphor of the display screen for a particular color can vary from screen to screen. If the phosphor has different characteristics, then its color intensity will vary from screen to screen thereby producing screens with different color balance. Therefore, it is important that a display screen have a mechanism for altering the relative color intensities of the color points so that manufacturing variations in the phosphor can be compensated for in the display screen. The method of altering the relative color intensities of the color points across a display screen is called white balance adjustment (also referred to as color balance adjustment or color temperature adjustment).
Another reason for providing color balance adjustment, in addition to correcting for manufacturing variations in the phosphor, is to correct for phosphor aging through prolonged display use. It is typical for the light emitting characteristics of the phosphor of an FED screen to change over time as it is used. Therefore, it is important that a display screen have a mechanism for altering its color balance to correct for phosphor aging to maintain image quality throughout the life of the FED screen. A further reason for providing color balance adjustment within a display screen is to allow the viewer to manually adjust the color balance. Using a manual adjustment, users can adjust the white balance of the display screen to their particular viewing taste.
One method for correcting or altering the color balance within a display screen is to alter, on the fly, the color data used to render a screen. Instead of sending a particular color point a color value of X, the color value of X is first passed through a function that has complex gain and offset adjustments. The output of the function, Y, is then sent to the color point. The function compensates for any variations in the color temperature caused by phosphor variations. The gain and offset factors of the above function can be altered as the color temperature needs to be increased or decreased. Although offering dynamic color balance adjustment, this prior art mechanism for altering the color balance is disadvantageous because it requires relatively complex circuitry for altering a relatively large volume of color data. For instance, in order to represent the color balance function, a look-up table (LUT) is used for each column.
The additional circuitry (e.g., a LUT) that this prior art mechanism requires adds significantly to the overall size of the driver circuits and negatively impacts performance speed. Assuming a horizontal screen resolution of 1024 white pixels, there can be as many as 3072 column drivers per FED screen and a complex LUT circuit replicated over 3072 column drivers may require too much substrate area for practical fabrication. Secondly, this prior art mechanism may degrade the quality of the image by reducing the gray-scale resolution of the flat panel display. It is desirable to provide a color balance adjustment mechanism for a flat panel display screen that does not alter the image data nor compromise the gray-scale resolution of the image.
Another method of correcting for color balance within a flat panel display screen is used in active matrix flat panel display screens (AMLCD). This method pertains to altering the physical color filters used to generate the red, green and blue color points. By altering the color the filters, the color temperature of the AMLCD screen can be adjusted. However, this adjustment is not dynamic because the color filters need to be physically (e.g., manually) replaced each time adjustment is required. It would be advantageous to provide a color balancing mechanism for a flat panel display screen that can respond, dynamically, to required changes in the color temperature of the display.
FIG. 1 illustrates a graph 6 of a typical data-in voltage-out curve that is embedded within a digital to analog converter circuit of an AMLCD flat panel display. The digital to analog converter is responsible for transforming the digital color data to voltages that are used to generate the actual color intensity. When presented with color data from 0 to 63, the voltages corresponding to curve portion 2 are supplied as output to drive the color points. When presented with color data from 64 to 127, the voltages corresponding to curve portion 4 are supplied as output to drive the color points. Curve portion 4 may be the same as curve portion 2 except with a DC voltage offset. Curve portion 4 and curve portion 2 are used in alternating refresh cycles so that no net DC voltage is applied to the cells of the AMLCD display. Prolonged exposure to DC voltage can destroy the AMLCD display. Therefore, the gray scale resolution of the AMLCD device using curves 2 and 4 is only from 0 to 63, although 127 data positions exist. This is the case because positions 64 to 127 are only duplicates, respectively, of positions 0 to 63. Although used in the manner described above, the data-in voltage-out function of FIG. 1 has never been applied to perform any type of color balancing operations.
Accordingly, the present invention provides a mechanism and method for dynamically adjusting the color balance of a flat panel display. The present invention provides a mechanism and method for adjusting the color balance of a flat panel display screen that does not significantly compromise the gray-scale resolution of the pixels of the display screen. Further, the present invention provides a mechanism and method for adjusting the color balance of a flat panel display screen without significantly increasing the size of the column driver circuits. Further, the present invention provides a mechanism and method for controlling the color balance of a flat panel FED screen while providing a power savings operational mode. These and other advantages of the present invention not specifically mentioned above will become clear within discussions of the present invention presented herein.